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Old 20-04-2003, 06:23 AM
David Lloyd
Posts: n/a
Default water testing, and a chemistry lesson

) wrote in message . com...
Okay, baking soda is sodium bicarbonate (Na^+ HCO3^-), so the addition
of that will increase KH as bicarbonate concentration has increased.
CO2 dissolves in water to form hydrogen bicarbonate (bicarbonic acid):

CO2 + H2O --- H^+ HCO3^-

Okay so you mean H2CO3.
Not the bicarbonate ion -HCO3?

I think there's some confusion there on those two terms.

Maybe a little (it's a while since I had to think about these sorts of
things), but I did mean the bicarbonate anion.

I'll just explain that I'm a newbie when it comes to aquaria. I have a
scientific background but am slightly baffled by the use of "GH" and
"KH" as terms, so I may be barking up some very wrong trees here!

Here's what I understand...

CO2 dissolves in water to form carbonic acid (my terminology above was
flavoured a little by forgetfulness and therefore a little misleading,
I agree):

CO2(g) + H2O --- CO2(aq) + H2O --- H2CO3

But it doesn't stop there...

H2CO3 --- (H^+) + (HCO3^-) --- 2(H^+) + (CO3^2-)

I don't use pure water in my relatively new aquarium. I use water that
comes from my kitchen sink. We have

pH 7.6
18 dGH
11 dKH
0 ppm NH3/NH4^+
0 ppm NO2^-
20 ppm NO3^-

At pH 7.6 more than 90% of the CO2 that forms H2CO3 will wind up in
the HCO3^- state. HCO3^- is the dominant state between around pH 6.5
and pH 10.

I'm not sure I know what "KH" is. My gut feeling is that it is
supposed to indicate bicarbonate and carbonate concentrations in
solution, but I'm also pretty sure that I'm not measuring this when I
use my test kit